Conveyor belts are used in a variety of industries to transport goods and materials from one place to another. Generally, goods are deposited at one end of a conveyor and are transported to the other end, where they are discharged or otherwise removed from the conveyor belt. The belts used are often robust, but are susceptible to damage from a variety of sources. While the discharge of the goods from a conveyor belt does not usually cause damage to the belt, the act of depositing goods and materials onto a conveyor belt has the potential to cause damage. In this regard, when a belt is being used to transport coal, aggregate and other coarse and heavy material, the deposit of these types of rocks onto the belt can generate tremendous impact forces on the belt. For instance, with a 100 lb mass having drop distance of 10 feet from a discharge chute onto a conveyor belt, there is 1,000 ft-pounds of force impacting the belt.
An impact bed is an apparatus which is installed below the area of a conveyor belt on which heavy loads are deposited for absorbing the impact forces generated thereby, as discussed above. Generally, impact beds can be classified as either static or dynamic. Static impact beds have resilient impact bars and an underlying bed framework that includes rigidly connected frame members. For instance, static impact beds typically include at least two support members for supporting the resilient impact bars thereon with the support members extending from either side of the belt inwardly and toward the middle of the belt. The support members are rigidly secured on cross members that span the width of the belt to be rigidly secured to stringers of the conveyor belt frame.
By contrast, dynamic impact beds differ from static impact beds in the manner in which impact forces are absorbed since, rather than using resilient impact bars, dynamic impact beds have torsion bias units mounted under an impact cradle upon which the belt is supported. In this regard, unlike static beds, the bed framework underlying the impact cradles includes frame members resiliently connected together via the torsion bias units secured therebetween.
Generally, there is a trade off between increasing the capacity of the bed to absorb impact forces, such as by using thicker impact bars with static impact beds, and the size of the impact bed. In other words, an impact bed having a compact size for fitting under the belt generally sacrifices in its ability to absorb high impact forces. Given that an impact bed is meant to be installed under the upper or carry run of a belt, a location often without an excess of space, balancing the size and strength of the bed is important. Generally, the vertical height between the carry run of the belt and the upper surface of the conveyor frame stringer member currently is approximately 8.5 to approximately 9.0 inches and cost constraints may tend to shrink the size of this space even further.
In typical static impact beds, several sets of support members will be longitudinally spaced from each other under the area of the belt where materials are deposited thereon for being conveyed thereby. The longitudinally spaced support members have the resilient bars secured thereto to extend thereacross running lengthwise in the belt travel direction and which are operable to absorb the impact forces and to decrease the acceleration of the materials or rocks dropped onto the belt. The resilient bars are subject to wear and damage over repeated impacts with the belt and thus need to be serviced and/or replaced on a regular basis.
In many static impact beds, servicing of the impact bars, particularly for those in the lower central area under a troughed belt, requires that the loading on the impact bed by the heavy conveyor belt thereon be relieved. This allows an operator to unfasten the support members from the cross members so that the support members and impact bars thereon can be removed out from under the belt for servicing.
In some prior static impact beds, the support members upon which the impact bars are secured can be slid in and out from under the conveyor belt along the cross members. However, when the support members are slid out from under the conveyor belt, the relatively heavy support members and impact bars thereon, e.g. approximately 100 to 200 lbs., must be supported, such as by heavy equipment like a crane or other lifting or support mechanism, which allows an operator to safely replace the impact bars.
In prior static impact beds, the support members are secured in their operative positions under the belt by being bolted to the cross members. This requires that an operator reach or climb under the belt to access the bolt locations, which can be of particular difficulty when the bolting needs to occur centrally under a troughed belt at which the belt is at its lowest height and where there is very little work space available between the upper and lower runs of the belt. Similar problems are presented when servicing of the impact bed is necessary and the securing bolts need to be removed.
Thus, prior static impact beds suffer from problems with optimizing size of the bed and their impact absorption capacity, and from difficulty in servicing the resilient impact bars.
Known dynamic impact beds differ from static beds by the provision of torsion bias units, such as Rosta mounts, between the cross members and the upper impact cradles of the beds. In one known dynamic impact bed, the Rosta mounts are secured on elevated platforms extending up from the cross member and connected to outer ends of the support members thereover. In another known dynamic impact bed, a pair of Rosta mounts are linked together, with the lower unit secured to the cross member and the upper unit secured to the impact cradle. In both instances, the profile of the dynamic impact bed above the cross members is undesirably increased due to the location of the Rosta mounts under the belt and over the cross members. In this regard, the impact cradles typically need to have a very low profile and thus utilize low profile impact plates that engage under the belt instead of the thicker, resilient impact bars used with static impact beds.